Figure 5.

Overall energetic models for a complete foraging bout, calculated for total flight times of 100 s and 900 s and assuming a nectar (sucrose solution) load of 105 µl and bee mass of 163 mg. The rate of energy return to the nest is maximized at a sucrose concentration of 65% for a foraging bout with a flight time of 100 s and 74% for a flight time of 900 s (solid lines). The effect of excluding the viscosity dependence of sucrose offloading is illustrated by the dashed line; this is also for a flight time of 100 s but with a fixed offloading time across all concentrations and raises the concentration at which the rate of energy return is maximized to 68%. (Online version in colour.)